Microbattery separator

ABSTRACT

In one example, a battery includes a negative terminal, a positive terminal, an electrolyte contained between the negative terminal and the positive terminal, and a hydrogel layer positioned between and physically separating the negative terminal and the positive terminal.

FIELD OF THE DISCLOSURE

The present disclosure relates generally to electric batteries andrelates more specifically to a separator for use in microbatteries.

BACKGROUND OF THE DISCLOSURE

All electrochemical cells or batteries contain a negative terminal (ananode) and a positive terminal (a cathode) that are separated from eachother by an electrolyte. When a battery is connected to an externalcircuit, the electrolyte is able to move as ions within the battery, andchemical reactions occur at each terminal that deliver energy to theexternal circuit.

Physical separation of the positive terminal from the negative terminalis maintained by a permeable membrane or separator. Historically,separators have been fabricated from non-woven materials such as paper,porous rubber, celluloid, or cellophane. More recently, separators havebeen fabricated from some non-woven non-cellulosic polymers, includingpolyamides, polyvinyl alcohol (PVOH), polyesters, and polypropylenes.

SUMMARY OF THE DISCLOSURE

In one example, a battery includes a negative terminal, a positiveterminal, an electrolyte contained between the negative terminal and thepositive terminal, and a hydrogel layer positioned between andphysically separating the negative terminal and the positive terminal.

In another example, a method of fabricating a battery includes forming anegative terminal, fabricating a separator on the negative terminal,wherein the separator comprises a hydrogel, forming a positive terminalon the separator, so that the separator physically separates thenegative terminal from the positive terminal, and injecting anelectrolyte between the negative terminal and the positive terminal

BRIEF DESCRIPTION OF THE DRAWINGS

The teachings of the present disclosure can be readily understood byconsidering the following detailed description in conjunction with theaccompanying drawings, in which:

FIGS. 1A-1F illustrate cross sectional views of a microbattery structureduring various stages of a first fabrication process performed accordingto examples of the present disclosure;

FIGS. 2A-2F illustrate cross sectional views of a microbattery structureduring various stages of a second fabrication process performedaccording to examples of the present disclosure; and

FIGS. 3A-3F illustrate cross sectional views of a microbattery structureduring various stages of a third fabrication process performed accordingto examples of the present disclosure.

To facilitate understanding, identical reference numerals have beenused, where possible, to designate identical elements that are common tothe Figures.

DETAILED DESCRIPTION

In one example, a separator for use in microbatteries is disclosed.Within the context of the present invention, a “microbattery” describesa cell that is, at most, a few hundred microns thick and whose activeelectrode areas are on the order of a few square millimeters. In suchbatteries, many of the components (including current collectors, activeanode metal, contact pads, and seals) may be most amenable tofabrication by photolithography.

Battery separators have conventionally been fabricated from non-wovenmaterials such as paper, porous rubber, celluloid, or cellophane, andmore recently from some non-woven non-cellulosic polymers, includingpolyamides, polyvinyl alcohol (PVOH), polyesters, and polypropylenes.These separators are typically made available as thin sheets deliveredon rolls. Although such delivery is convenient for the production oflarge commercial batteries in standard cylindrical form factors (e.g.,AA, AAA, button cells, coin cells, and the like), it is less suited tothe production of very small, thin, flexible microbatteries. Forinstance, it is difficult and highly impractical to attempt to introducea thin piece of sheet separator into a microbattery structure byphysically picking and placing the separator into the space between thepositive and negative terminals.

Examples of the present disclosure provide microbattery separators thatare aligned to the features of the positive and negative terminals andthat are process compatible with the fabrication build of themicrobattery. Examples of the disclosed separator can be formed from ahydrogel, a photopatterned polymer mesh, or a combination of a hydrogeland a photo-patterned polymer mesh.

FIGS. 1A-1F illustrate cross sectional views of a microbattery structure100 during various stages of a first fabrication process performedaccording to examples of the present disclosure. As such, when viewed insequence, FIGS. 1A-1F also serve as a flow diagram for the fabricationprocess.

As illustrated in FIG. 1A, fabrication of the microbattery structure 100begins by bonding a first polymer film layer 104 to a first glasssubstrate 102. In one example, the first polymer film layer 104comprises a polyimide, such as poly(4,4′-oxydiphenylene-pyromellitimide), or polyethylene terephthalate(PET).

As illustrated in FIG. 1B, a trench is next created in the first polymerfilm layer 104. The trench may be formed, for example, byphotolithography in combination with etching, or by embossing. Thetrench is subsequently lined with a first conformal metal layer 106. Thefirst conformal metal layer 106 may be formed, for example, fromtitanium or from nickel.

As illustrated in FIG. 1C, a negative terminal 108 is next plated on thefirst conformal metal layer 106, within the trench area. The negativeterminal 108 may be formed, for example, from zinc, or from an alloy ofzinc with indium or with tin. A hydrogel layer 110 is then applied tothe negative terminal 108. For instance, the hydrogel layer 110 may beapplied by precision dispensing, stenciling, injecting, or brushing ontothe negative terminal 108. In one example, the hydrogel comprises anetwork of polymer chains that are hydrophilic. For instance, thehydrogel may comprise a colloidal gel in which water is the dispersionmedium. As a specific example, the hydrogel may comprise apolyethylglycol (PEG)-based system with water and a photocatalyst, apolyvinylpyrrolidone (PVP)-based system with a photocatalyst,polyethylene oxide (PEO), poly vinyl alcohol (PVA), or polyacrylamide.In one example, the hydrogel layer 110 has a thickness of approximatelyten to twenty micrometers. The hydrogel layer 110 will form theseparator of the final microbattery structure 100.

As illustrated in FIG. 1D, a seal 112 is deposited on the firstconformal metal layer 106, outside of the trench, i.e., so that the seal112 surrounds the trench, the negative terminal 108, and the hydrogellayer 110. A positive terminal 114 is then deposited on the hydrogellayer 110 and compresses the hydrogel layer 110. The positive terminal114 may comprise, for example, a paste such as a manganese dioxide pastehaving particle sizes between approximately two and thirty micrometers.In further examples, however, the particle size can be even finer (e.g.,down to the sub-micron level). As the hydrogel layer 110 compresses, itis held in place by the seal 112 and by the positive terminal 114. Anelectrolyte is also injected into the microbattery structure 100 andbecomes absorbed by the hydrogel layer 110.

As illustrated in FIG. 1E, a pedestal is next fabricated, separatelyfrom the microbattery structure 100 that was assembled and depicted inFIGS. 1A-1D. Fabrication of the pedestal begins by bonding a secondpolymer film layer 118 to a second glass substrate 116. In one example,the second polymer film layer 118 comprises a polyimide, such as poly(4,4′-oxydiphenylene-pyromellitimide), or polyethylene terephthalate(PET). The second polymer film layer 118 may be etched to form a mesa orpedestal in its center, as illustrated. The second polymer film layer118 is then coated with a second conformal metal layer 120. The secondconformal metal layer 120 may comprise, for example, titanium, nickel,or indium tin oxide.

As illustrated in FIG. 1F, the pedestal illustrated in FIG. 1E is thenassembled to the microbattery structure 100 that was assembled anddepicted in FIGS. 1A-1D to seal the microbattery structure 100. In oneexample, this assembly step involves inverting the pedestal such thatthe second conformal metal layer 120 is positioned adjacent to the seal112 and the positive terminal 114. In one example, the second glasssubstrate 116 is removed.

The hydrogel layer 110 of the microbattery structure 100 acts as apermeable separator between the negative terminal 108 and the positiveterminal 114. The hydrophilic nature of the hydrogel layer 110 allows itto absorb the electrolyte that resides between the negative terminal 108and the positive terminal 114, while the inclusion of a photocatalyst inthe hydrogel layer 110 will allow the hydrogel layer 110 to be cured orcross-linked, e.g., such that the hydrogel layer 110 can be patternedwhere desired. The flexibility of and the ability to precisely apply thehydrogel layer 110 during fabrication of the microbattery structure 100makes it an ideal separator for the very small scale microbatterystructure 100. For instance, photolithography techniques may be used todefine and align very small features with precision.

FIGS. 2A-2F illustrate cross sectional views of a microbattery structure200 during various stages of a second fabrication process performedaccording to examples of the present disclosure. As such, when viewed insequence, FIGS. 2A-2F also serve as a flow diagram for the fabricationprocess.

As illustrated in FIG. 2A, fabrication of the microbattery structure 200begins by bonding a first polymer film layer 204 to a first glasssubstrate 202. In one example, the first polymer film layer 204comprises polyimide, such as poly (4,4′-oxydiphenylene-pyromellitimide),or polyethylene terephthalate (PET).

As illustrated in FIG. 2B, a trench is next created in the first polymerfilm layer 204. The trench may be formed, for example, byphotolithography in combination with etching, or by embossing. Thetrench is subsequently lined with a first conformal metal layer 206. Thefirst conformal metal layer 206 may be formed, for example, fromtitanium or from nickel.

As illustrated in FIG. 2C, a negative terminal 208 is next plated on thefirst conformal metal layer 206, within the trench area. The negativeterminal 208 may be formed, for example, from zinc, or from an alloy ofzinc with indium or with tin. A photo-patternable polymer layer 210 isthen applied to the negative terminal 208, for example by a spin coatingprocess in which a photo-patternable polymer is applied in liquid form(e.g., in a range of approximately 750 to 3000 rpm), and excess liquidfrom the photo-patternable polymer is spun off the top surface of thenegative terminal 208. In one example, this results in thephoto-patternable polymer layer 210 having a thickness of approximatelytwo micrometers; thus, the raised topography of the negative terminal208 in this case allows for a thinner coating of the photo-patternablepolymer to be applied to the negative terminal 208 (i.e., as compartedto the remainder of the microbattery structure 200). Thephoto-patternable polymer layer 210 is then patterned into a mesh, forexample using a photolithography process. In one example, thephoto-patternable polymer layer 210 may be soft-baked (i.e.,pre-exposure) and/or post-exposure baked at a temperature within therange of approximately sixty-five to one hundred degrees Celsius, whilea final hard bake may be performed at a temperature in the range ofapproximately 150 to 250 degrees Celsius. Thus, the finalphoto-patternable polymer layer 210 comprises a polymer mesh that iscoated, aligned, and patterned in a manner similar to photoresist in asemiconductor line. The mesh may contain pores having a size ofapproximately two micrometers square. In one example, thephoto-patternable polymer layer 210 comprises a phenoxy-based resin(e.g., one or more of a family of Bisphenol-A/epichlorohydrin linearpolymers). For instance, the photo-patternable polymer layer 210 maycontain a mixture of an epoxy, a phenoxy-based resin, and a solvent suchas propylene glycol monomethyl ether acetate. The phenoxy-based resinmay further include a photo-package to enable lithographic processing.The photo-patternable polymer layer 210 will form the separator of thefinal microbattery structure 200.

As illustrated in FIG. 2D, a seal 212 is deposited on the firstconformal metal layer 206, outside of the trench, i.e., so that the seal212 surrounds the trench, the negative terminal 208, and thephoto-patternable polymer layer 210. An electrolyte 216 is injected intothe microbattery structure 200 and is able to pass through the mesh ofthe photo-patternable polymer layer 210. A positive terminal 214 is thendeposited on the photo-patternable polymer layer 210. The positiveterminal 214 may comprise, for example, a paste such as a manganesedioxide paste having particle sizes between approximately two and thirtymicrometers. The mesh structure of the photo-patternable polymer layer210 prevents particles of the paste from clogging or breaking throughthe photo-patternable polymer layer 210 and contacting the negativeterminal 208.

As illustrated in FIG. 2E, a pedestal is next fabricated, separatelyfrom the microbattery structure 200 that was assembled and depicted inFIGS. 2A-2D. Fabrication of the pedestal begins by bonding a secondpolymer film layer 220 to a second glass substrate 218. In one example,the second polymer film layer 220 comprises a polyimide, such as poly(4,4′-oxydiphenylene-pyromellitimide), or polyethylene terephthalate(PET). The second polymer film layer 220 may be etched to form a mesa orpedestal in its center, as illustrated. The second polymer film layer220 is then coated with a second conformal metal layer 222. The secondconformal metal layer 222 may comprise, for example, titanium, nickel,or indium tin oxide.

As illustrated in FIG. 2F, the pedestal illustrated in FIG. 2E is thenassembled to the microbattery structure 200 that was assembled anddepicted in FIGS. 2A-2D to seal the microbattery structure 200. In oneexample, this assembly step involves inverting the pedestal such thatthe second conformal metal layer 222 is positioned adjacent to the seal212 and the positive terminal 214. In one example, the second glasssubstrate 218 is removed.

The mesh photo-patternable polymer layer 210 of the microbatterystructure 200 acts as a permeable separator between the negativeterminal 208 and the positive terminal 214. The mesh structure of thephoto-patternable polymer layer 210 allows the electrolyte that residesbetween the negative terminal 208 and the positive terminal 214 to passfreely, while maintaining mechanical separation between the negativeterminal 208 and the positive terminal 214. The ability to preciselyapply and pattern the photo-patternable polymer layer 210 duringfabrication of the microbattery structure 200 makes it an idealseparator for the very small scale microbattery structure 200. Forinstance, photolithography techniques may be used to define and alignvery small features with precision.

In a further example, the techniques illustrates in FIGS. 1A-1F andFIGS. 2A-2F can be combined to obtain the advantages of both thehydrogel and the photo-patternable polymer as a separator. FIGS. 3A-3Fillustrate cross sectional views of a microbattery structure 300 duringvarious stages of a third fabrication process performed according toexamples of the present disclosure. As such, when viewed in sequence,FIGS. 3A-3F also serve as a flow diagram for the fabrication process.

As illustrated in FIG. 3A, fabrication of the microbattery structure 300begins by bonding a first polymer film layer 304 to a first glasssubstrate 302. In one example, the first polymer film layer 304comprises a polyimide, such as poly(4,4′-oxydiphenylene-pyromellitimide), or polyethylene terephthalate(PET).

As illustrated in FIG. 3B, a trench is next created in the first polymerfilm layer 304. The trench may be formed, for example, byphotolithography in combination with etching, or by embossing. Thetrench is subsequently lined with a first conformal metal layer 306. Thefirst conformal metal layer 306 may be formed, for example, fromtitanium or nickel.

As illustrated in FIG. 3C, a negative terminal 308 is next plated on thefirst conformal metal layer 306, within the trench area. The negativeterminal 308 may be formed, for example, from zinc, or from an alloy ofzinc with indium or with tin. A photo-patternable polymer layer 310 isthen applied to the negative terminal 308, for example by a spin coatingprocess in which a photo-patternable polymer is applied in liquid form(e.g., in a range of approximately 750 to 3000 rounds per minute), andexcess liquid from the photo-patternable polymer is spun off the topsurface of the negative terminal 308. In one example, this results inthe photo-patternable polymer layer 310 having a thickness ofapproximately two micrometers; thus, the raised topography of thenegative terminal 308 in this case allows for a thinner coating of thephoto-patternable polymer to be applied to the negative terminal 308(i.e., as comparted to the remainder of the microbattery structure 300).The photo-patternable polymer layer 310 is then patterned into a mesh,for example using a photolithography process. In one example, thephoto-patternable polymer layer 310 may be soft-baked (i.e.,pre-exposure) and/or post-exposure baked at a temperature within therange of approximately sixty-five to one hundred degrees Celsius, whilea final hard bake may be performed at a temperature in the range ofapproximately 150 to 250 degrees Celsius. Thus, the finalphoto-patternable polymer layer 310 comprises a polymer mesh that iscoated, aligned, and patterned in a manner similar to photoresist in asemiconductor line. The mesh may contain pores having a size ofapproximately two micrometers square. In one example, thephoto-patternable polymer layer 310 comprises a phenoxy-based resin(e.g., one or more of a family of Bisphenol-A/epichlorohydrin linearpolymers). For instance, the photo-patternable polymer layer 310 maycontain a mixture of an epoxy, a phenoxy-based resin, and a solvent suchas propylene glycol monomethyl ether acetate. The phenoxy-based resinmay further include a photo-package to enable lithographic processing.

In addition, a hydrogel layer 316 is applied to fill the pores of thephoto-patternable polymer layer 310 and to increase the overallhydrophilicity of the mesh. For instance, the hydrogel layer 316 may beapplied by precision dispensing, stenciling, injecting, or brushing ontothe photo-patternable polymer layer 310. In one example, the hydrogelcomprises a network of polymer chains that are hydrophilic. Forinstance, the hydrogel may comprise a colloidal gel in which water isthe dispersion medium. As a specific example, the hydrogel may comprisea polyethylglycol (PEG)-based system with water and a photocatalyst, apolyvinylpyrrolidone (PVP)-based system with a photocatalyst,polyethylene oxide (PEO), poly vinyl alcohol (PVA), or polyacrylamide.In one example, the hydrogel layer 316 has a thickness of approximatelyten to twenty micrometers. The hydrogel layer 316, in combination withthe photo-patternable polymer layer 310, will form the separator of thefinal microbattery structure 300.

As illustrated in FIG. 3D, a seal 312 is deposited on the firstconformal metal layer 306, outside of the trench, i.e., so that the seal312 surrounds the trench, the negative terminal 308, thephoto-patternable polymer layer 310, and the hydrogel layer 316. Anelectrolyte is injected into the microbattery structure 300 and absorbedby the hydrogel layer 316. A positive terminal 314 is then deposited onthe photo-patternable polymer layer 310 and hydrogel layer 316. As thehydrogel layer 316 is compressed by the positive terminal 314, it isheld in place by the seal 312, by the positive terminal 314, and by thephoto-patternable polymer layer 310. The positive terminal 314 maycomprise, for example, a paste such as a manganese dioxide paste havingparticle sizes between approximately two and thirty micrometers. Infurther examples, the inclusion of the hydrogel layer 316 allows theparticle sizes of the paste to be even smaller, since the hydrogel willprevent the particles from passing through the pores of the meshphoto-patternable polymer layer 310. Thus, the particles of the pastemay even be smaller than the pores of the mesh.

As illustrated in FIG. 3E, a pedestal is next fabricated, separatelyfrom the microbattery structure 300 that was assembled and depicted inFIGS. 3A-3D. Fabrication of the pedestal begins by bonding a secondpolymer film layer 320 to a second glass substrate 318. In one example,the second polymer film layer 320 comprises a polyimide, such as poly(4,4′-oxydiphenylene-pyromellitimide), or polyethylene terephthalate(PET). The second polymer film layer 320 may be etched to form a mesa orpedestal in its center, as illustrated. The second polymer film layer320 is then coated with a second conformal metal layer 322. The secondconformal metal layer 322 may comprise, for example, titanium, nickel,or indium tin oxide.

As illustrated in FIG. 3F, the pedestal illustrated in FIG. 3E is thenassembled to the microbattery structure 300 that was assembled anddepicted in FIGS. 3A-3D to seal the microbattery structure 300. In oneexample, this assembly step involves inverting the pedestal such thatthe second conformal metal layer 322 is positioned adjacent to the seal312 and the positive terminal 314. In one example, the second glasssubstrate 318 is removed.

The combination of the mesh photo-patternable polymer layer 310 and thehydrogel layer 316 acts as a permeable separator between the negativeterminal 308 and the positive terminal 314 of the microbattery structure300. The mesh structure of the photo-patternable polymer layer 310allows the electrolyte, which is absorbed by the hydrogel layer 316, topass freely between the negative terminal 308 and the positive terminal314, while maintaining mechanical separation between the negativeterminal 308 and the positive terminal 314. The ability to preciselyapply and/or pattern the photo-patternable polymer layer 310 and thehydrogel layer 316 during fabrication of the microbattery structure 300makes it an ideal separator for the very small scale microbatterystructure 300.

Although various embodiments which incorporate the teachings of thepresent invention have been shown and described in detail herein, thoseskilled in the art can readily devise many other varied embodiments thatstill incorporate these teachings.

What is claimed is:
 1. A method of fabricating a battery, comprising:forming a first polymer film layer; forming a trench in the firstpolymer film layer; lining the trench with a first conformal metallayer; forming a negative terminal in the trench, such that the firstconformal metal layer is positioned directly between the first polymerfilm layer and the negative terminal; fabricating a separator on thenegative terminal, wherein the separator comprises a hydrogel, whereinthe hydrogel is comprised of a polyethylglycol-based system of water;forming a positive terminal on the separator, so that the separatorphysically separates the negative terminal from the positive terminal;and injecting an electrolyte between the negative terminal and thepositive terminal.
 2. The method of claim 1, wherein the fabricating theseparator comprises: precision dispensing the hydrogel onto the negativeterminal.
 3. The method of claim 1, wherein the fabricating theseparator comprises: stenciling the hydrogel onto the negative terminal.4. The method of claim 1, wherein the fabricating the separatorcomprises: injecting the hydrogel onto the negative terminal.
 5. Themethod of claim 1, wherein the fabricating the separator comprises:brushing the hydrogel onto the negative terminal.
 6. The method of claim1, wherein the separator further comprises a patterned polymer mesh, andthe hydrogel fills pores of the patterned polymer mesh.
 7. The method ofclaim 1, wherein the separator further comprises a patterned polymermesh, and the hydrogel fills pores of the patterned polymer mesh.
 8. Themethod of claim 7, wherein the photo-patternable polymer comprises aphenoxy-based resin.
 9. The method of claim 8, wherein thephoto-patternable polymer further comprises a photo-package.
 10. Themethod of claim 6, wherein the patterned polymer mesh has a pore size oftwo micrometers square or smaller.
 11. The method of claim 1, whereinthe electrolyte is absorbed in the hydrogel.
 12. The method of claim 1,wherein the hydrogel includes a photocatalyst.
 13. The method of claim1, wherein the hydrogel has a thickness of between ten and twentymicrometers.
 14. A method of fabricating a battery, comprising: forminga first polymer film layer; forming a trench in the first polymer filmlayer; lining the trench with a first conformal metal layer; forming anegative terminal in the trench, such that the first conformal metallayer is positioned directly between the first polymer film layer andthe negative terminal; fabricating a separator on the negative terminal,wherein the separator comprises a hydrogel; forming a positive terminalon the separator, so that the separator physically separates thenegative terminal from the positive terminal; injecting an electrolytebetween the negative terminal and the positive terminal; forming asecond conformal metal layer positioned adjacent to the positiveterminal, and forming a second polymer film layer, wherein the secondconformal metal layer is positioned directly between the second polymerfilm layer and the positive terminal.
 15. The method of claim 14,further comprising: surrounding the negative terminal and the hydrogelwith a seal, wherein the first conformal metal layer is positioneddirectly between the first polymer film layer and the seal; andpositioning the second conformal metal layer directly between the secondpolymer film layer and the seal.
 16. The method of claim 15, furthercomprising: forming a mesa in the second polymer film layer.
 17. Themethod of claim 15, wherein the electrolyte is absorbed in the hydrogel.18. The method of claim 14, wherein the separator further comprises apatterned polymer mesh, and the hydrogel fills pores of the patternedpolymer mesh.
 19. The method of claim 18, wherein the fabricating theseparator comprises: spin coating a layer of a photo-patternable polymerin liquid form onto the negative terminal; patterning the layer of thephoto-patternable polymer, using a photolithography technique, to formthe patterned polymer mesh.
 20. The method of claim 14, wherein thehydrogel comprises a polyethylglycol-based system with water.